Chapter 15.5, Problem 52SSC

Interpretation Introduction

Interpretation:

The concept of spontaneous and non-spontaneous reaction is to be discussed.

Concept introduction:

The concept of spontaneous and non-spontaneous reaction is discussed in the section.

Answer to Problem 52SSC

Spontaneous and non-spontaneous reactions:

Spontaneous reactions:

A reaction that can take place of its own or by some initiation

For example- Carbon monoxide is oxidized to carbon dioxide of its own.

Non-spontaneous reactions:

A reaction that can’t take place even by strong initiation

For example- No reaction takes place when silver chloride and sodium nitrate are mixed.

Concept of entropy:

Entropy is the degree of randomness of a system.

It is denoted by ‘S’

Universe always tries to increase its entropy.

For a reaction, $\Delta S_{system}=S_{products}-S_{reac\tan ts}$

Free energy:

Free energy is the amount of energy available for doing useful work.

It is denoted by ‘G’

For a reaction,

$\Delta G=\Delta H-T\Delta S$

Effect of temperature on reaction spontaneity:

$\Delta H_{system}$	$\Delta S_{system}$	$\Delta G_{system}$	Spontaneity of reaction
negative	positive	Always negative	Always spontaneous
negative	negative	Negative or positive	Spontaneous at lower temperatures
positive	positive	Negative or positive	Spontaneous at higher temperatures
positive	negative	Always positive	Never spontaneous

Explanation of Solution

	Spontaneous reactions	Non-spontaneous reactions
Definition	A reaction that can take place of its own or by some initiation	A reaction is that can’t take place even by strong initiation.
Gibbs free energy change	$\Delta G<0$	$\Delta G>0$
Enthalpy change	Generally, $\Delta H<0$	Generally, $\Delta H>0$
Entropy change	Generally, $\Delta S>0$	Generally, $\Delta S<0$
Effect of Temperature	Exothermic reactions favored at low temperature and Endothermic reactions favored at high temperature	-----

Conclusion

Thus important ideas are:

• Entropy is a measure of disorder of the system.
• Spontaneous reactions always result in increase in entropy.
• Free energy is the energy available to do work.